This invention relates to novel meltblown webs with improved properties. In one aspect, the invention relates to a meltblown filter useful in filtration of gases such as air.
Meltblown nonwoven webs are made by the meltblowing process which involves extruding a thermoplastic resin through a row of closely spaced orifices to form a plurality of polymer filaments (or fibers) while converging sheets of high velocity hot air impart drag forces on the filaments and draw them down to microsized diameters. The microsized fibers are blown onto a collector screen or conveyor where they are entangled and collected, forming an integrated nonwoven web. The average diameter size of the fibers in the web range from about 0.5 to about 20 microns. Integrity or strength of the web depends upon the mechanical entanglement of the fibers as well as fiber bonding.
Meltblown webs are ideally suited for a variety of applications due to their microdenier fiber structure. Web properties which are important in these applications include:
(a) web bursting strength;
(b) packing density;
(c) web tenacity; and
(d) web elongation at break.
In addition, for filter applications the meltblown web should exhibit high filtration efficiency at reasonable air permeabilities.
As described in detail below, the present invention relates to a meltblown web which exhibits the properties mentioned above. The inventive web may be manufactured by a variety of processes, but the preferred process is by application of a cross-flow as described in U.S. Pat. No. 5,075,068.
References which disclose the application of some medium to the air/fiber stream of a meltblowing process upstream of the collector include U.S. Pat. Nos. 3,806,289, 3,957,421, 4,594,202, and 4,622,259. None of these references, however, disclose a meltblown web having the properties of the web of the present invention.